Convert Redux custom middleware to TypeScript

app/soapbox/middleware/errors.js

@@ -1,20 +0,0 @@
-import { showAlertForError } from '../actions/alerts';
-
-const isFailType = type => type.endsWith('_FAIL');
-const isRememberFailType = type => type.endsWith('_REMEMBER_FAIL');
-
-const hasResponse = error => Boolean(error && error.response);
-
-const shouldShowError = ({ type, skipAlert, error }) => {
-  return !skipAlert && hasResponse(error) && isFailType(type) && !isRememberFailType(type);
-};
-
-export default function errorsMiddleware() {
-  return ({ dispatch }) => next => action => {
-    if (shouldShowError(action)) {
-      dispatch(showAlertForError(action.error));
-    }
-
-    return next(action);
-  };
-}

app/soapbox/middleware/errors.ts

@@ -0,0 +1,29 @@
+import { showAlertForError } from '../actions/alerts';
+
+import type { AnyAction } from 'redux';
+import type { ThunkMiddleware } from 'redux-thunk';
+
+/** Whether the action is considered a failure. */
+const isFailType = (type: string): boolean => type.endsWith('_FAIL');
+
+/** Whether the action is a failure to fetch from browser storage. */
+const isRememberFailType = (type: string): boolean => type.endsWith('_REMEMBER_FAIL');
+
+/** Whether the error contains an Axios response. */
+const hasResponse = (error: any): boolean => Boolean(error && error.response);
+
+/** Whether the error should be shown to the user. */
+const shouldShowError = ({ type, skipAlert, error }: AnyAction): boolean => {
+  return !skipAlert && hasResponse(error) && isFailType(type) && !isRememberFailType(type);
+};
+
+/** Middleware to display Redux errors to the user. */
+export default function errorsMiddleware(): ThunkMiddleware {
+  return ({ dispatch }) => next => action => {
+    if (shouldShowError(action)) {
+      dispatch(showAlertForError(action.error));
+    }
+
+    return next(action);
+  };
+}

app/soapbox/middleware/sounds.ts

@@ -1,6 +1,15 @@
 'use strict';
 
-const createAudio = sources => {
+import type { ThunkMiddleware } from 'redux-thunk';
+
+/** Soapbox audio clip. */
+type Sound = {
+  src: string,
+  type: string,
+}
+
+/** Produce HTML5 audio from sound data. */
+const createAudio = (sources: Sound[]): HTMLAudioElement => {
   const audio = new Audio();
   sources.forEach(({ type, src }) => {
     const source = document.createElement('source');
@@ -11,7 +20,8 @@ const createAudio = sources => {
   return audio;
 };
 
-const play = audio => {
+/** Play HTML5 sound. */
+const play = (audio: HTMLAudioElement): void => {
   if (!audio.paused) {
     audio.pause();
     if (typeof audio.fastSeek === 'function') {
@@ -24,8 +34,9 @@ const play = audio => {
   audio.play();
 };
 
-export default function soundsMiddleware() {
-  const soundCache = {
+/** Middleware to play sounds in response to certain Redux actions. */
+export default function soundsMiddleware(): ThunkMiddleware {
+  const soundCache: Record<string, HTMLAudioElement> = {
     boop: createAudio([
       {
         src: require('../../sounds/boop.ogg'),
@@ -49,7 +60,7 @@ export default function soundsMiddleware() {
   };
 
   return () => next => action => {
-    if (action.meta && action.meta.sound && soundCache[action.meta.sound]) {
+    if (action.meta?.sound && soundCache[action.meta.sound]) {
       play(soundCache[action.meta.sound]);
     }